1. Field of the Invention
The present invention relates to a laminated composite, an information recording medium, and a member of imparting a forgery-preventing characteristic, and more particularly, to a laminated composite which can be used in discriminating an information recording medium between genuine one and a counterfeit by using a latent image, an information recording medium which can be discriminated between a genuine one and a counterfeit by using the latent image, a member of imparting, to an information recording medium, a forgery-preventing characteristic which enable discrimination of the information recording medium between a genuine one and a counterfeit.
2. Description of the Related Art
Conventionally, as techniques for preventing forgery of information recording mediums such as credit cards, securities, and certificates, methods using a latent image are known. The methods employ, for example,
1) A picture drawn by parallel lines: a latent image such as a hidden letter is drawn in a space between the parallel lines and the latent image can be visualized by concealing the parallel lines, and
2) A decomat: a latent image is formed by a printing technique using a transparent ink medium which contains a filler and the latent image can be visualized by rubbing the printed portion with a pencil so as to allow a powder from a lead of the pencil to attach onto the printed portion.
However, in methods 1) and 2), the latent image is legible if carefully observed. Thus, these methods 1) and 2) are used for pleasure rather than as a practical forgery-preventing technique.
As a more practical forgery-preventing technique, the following methods are known:
3) A method in which a latent image is formed by use of an irreversible thermochromic ink which is white or colorless and transparent and develops a color by application of heat.
4) A method in which a latent image is formed by a printing technique using a white ink which contains a filler such as titanium oxide harder than a metal, and the latent image can be visualized by rubbing the printed portion with a coin or the like.
However, the method 3) requires a heating device to visualize the latent image. In addition, once the latent image is visualized in the method 3), it cannot be returned to an invisible state. On the other hand, in the method 4), although the image such as a letter is rendered invisible by forming a mat-like varnish layer thereon, once the latent image is visualized, it cannot be returned to an invisible state. Therefore, the methods 3) and 4) can be used only once.
As a technique capable of repeating visualization and nonvisualization of a latent image, the following techniques are known.
5) A method in which a latent image is formed or a image is concealed by using a reversible thermochromic ink, which reversibly develops and loses a color thereof by application of heat and returns to its original state if left alone for a while.
6) A method in which a latent image is formed by using a photochromic ink, which is capable of developing a color by light irradiation, particularly, by ultraviolet irradiation, as the white or colorless and transparent ink; and
7) A method in which a latent image is formed by using an organic type or an inorganic type of fluorescent ink, which is capable of developing a color by ultraviolet irradiation, as the white or colorless and transparent ink.
However, the thermochromic ink used in the method 5) has a problem that the resistance thereof, particularly, the heat resistance, is low. The photochromic ink used in the method 6) also has a problem that the resistance thereof, particularly, the light stability is low.
When an organic fluorescent ink is used in the method 7), sufficient luminescence can be obtained simply by adding an extremely small amount of organic phosphor to a printing ink. However, the organic phosphor is low in light stability. Furthermore, when an inorganic fluorescent ink is used in the method 7), a large amount of inorganic phosphor (about 10-20%) need be added to a printing ink in order to obtain sufficient luminescence. Due to this, the latent image formed by using the inorganic fluorescent ink is apt to be legible by visual observation. Thus, the design of the latent image must be carefully made.
As mentioned above, methods 5)-7) are limited in application because of the resistance of ink.
As a forgery-preventing technique capable of repeating visualization and nonvisualization of the latent image, the following methods are known:
8) A method in which a latent image is formed by use of dots of a screen and moire fringes of parallel lines. In this method, the latent image is formed by partly changing the pitch of the dots or the pitch and/or angle of the parallel lines. Thereafter, a transparent film having regularly arranged dots or parallel lines thereon is overlaid on the latent image to visualize the latent image.
According to the method 8), the latent image can be visualized simply by using the transparent film. Thus, the visualization and non-visualization of the latent image can be easily repeated. In addition, this methods is free from the problem of resistance, so that application of the method is not limited. However, the method 8) has a problem that a complicated latent image cannot be obtained.
As another forgery-preventing method which can repeat the visualization and non-visualization of a latent image, the following method is known.
9) A method in which a latent image is formed by using a magnetic ink. In this method, a latent image is formed by partly magnetizing a magnetic layer which has a sufficiently high coersive force (about 300 Oe or more, or about 24 kA/m or more) enough to perform a magnetic recording, and the latent image is visualized by sprinkling an iron powder over the magnetic layer. However, in this method 9), a latent image can be easily rewritten and forged. In addition, the step of visualizing the latent image is complicated and requires a specific detection apparatus.
As another forgery-preventing technique which can repeat the visualization and nonvisualization of a latent image, the following method is known:
10) A method in which a latent image is formed by using an ink capable of absorbing infrared rays and a layer capable of transmitting the infrared rays and not transmitting visible light is formed on the latent image. However, this method requires an infrared camera etc. to visualize the latent image. Accordingly, the method has a problem that the apparatus inevitably increases in size. Another method is also known using a white or colorless ink (IV ink) absorbing infrared rays and not absorbing visible light. However, this method also requires an infrared camera etc.
According to the methods 9) and 10), it is possible to repeat the visualization and nonvisualization of a latent image and form a complicated latent image. In addition, there is no limitation in application due to resistance of the latent image. However, the methods 9) and 10) require a specific apparatus to visualize the latent image, as mentioned above.